title: Double-lock ratchet mechanism revealing the role of alphaSER-344 in FoF1 ATP synthase.
abstract: In a majority of living organisms, FoF1 ATP synthase performs the fundamental process of ATP synthesis. Despite the simple net reaction formula, ADP+Pi→ATP+H2O, the detailed step-by-step mechanism of the reaction yet remains to be resolved owing to the complexity of this multisubunit enzyme. Based on quantum mechanical computations using recent high resolution X-ray structures, we propose that during ATP synthesis the enzyme first prepares the inorganic phosphate for the γP-OADP bond-forming step via a double-proton transfer. At this step, the highly conserved αS344 side chain plays a catalytic role. The reaction thereafter progresses through another transition state (TS) having a planar ion configuration to finally form ATP. These two TSs are concluded crucial for ATP synthesis. Using stepwise scans and several models of the nucleotide-bound active site, some of the most important conformational changes were traced toward direction of synthesis. Interestingly, as the active site geometry progresses toward the ATP-favoring tight binding site, at both of these TSs, a dramatic increase in barrier heights is observed for the reverse direction, i.e., hydrolysis of ATP. This change could indicate a "ratchet" mechanism for the enzyme to ensure efficacy of ATP synthesis by shifting residue conformation and thus locking access to the crucial TSs.
authors.affiliation: Department of Chemical and Biological Engineering, Physical Chemistry, Chalmers University of Technology, SE-412 96 Göteborg, Sweden. beke@chalmers.se
authors.forename: Tamás
authors.initials: T
authors.lastname: Beke-Somfai
authors.forename: Per
authors.initials: P
authors.lastname: Lincoln
authors.forename: Bengt
authors.initials: B
authors.lastname: Nordén
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis / Q000737:chemistry*; D002384:Catalysis; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D006180:Proton-Translocating ATPases / Q000737:chemistry* / Q000378:metabolism; D012694:Serine / Q000737:chemistry* / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; D012694:Serine; D000255:Adenosine Triphosphate; D006180:Proton-Translocating ATPases